1. Field of the Invention
The subject invention relates generally to dampeners on offset lithographic printing presses, and, more particularly, to improved end-seal carriers on seal-type continuous dampeners.
2. Background of the Related Art
On a printing press utilizing the off-set lithographic method of printing there is typically required a dampener for applying dampening solution to a printing plate carried on a plate cylinder to ensure that the non-image area of the plate, and consequently the non-image area of the printed sheet, is kept clear of ink. An example of a dampener used on such printing presses is that disclosed in U.S. Pat. No. 4,455,938 (the '938 patent) to J. Loudon entitled DAMPENING APPARATUS FOR LITHOGRAPHIC PRESS, the disclosure of which is incorporated by reference. Dampeners represented by the '938 patent are described generally in the art as seal-type continuous dampeners.
The dampener apparatus described in the '938 patent essentially includes a form roller, a metering roller positioned parallel to and in contact with the form roller, and a set of side frames between which the rollers are rotationally supported. A V-shaped gap is formed above the line of contact between the form roller and metering roller. During printing operations the form roller is urged against the printing plate so as to apply dampening solution thereto.
Mounted to each side frame is an end-seal carrier. Each end-seal carrier is positioned proximate the point of contact between the form roller and metering roller for urging a pair of TEFLON end-seals against each end face of the form roller and against the outer surface each metering roller. In this position the seals `cap` the ends of the V-shaped gap forming a reservoir for the storage of fountain solution. As the rollers rotate, the seals wear so as to conform to the contour of the rollers that they contact, thereby creating a leak-proof fit between the seals and the rollers. Each end-seal carrier functions identically to, but is symmetrically opposite the other end-seal carrier to accommodate the rollers' configuration.
Considering only one end-seal carrier assembly, to properly urge a seal against the end of the form roller and the outside diameter of the metering roller, the end-seal carrier includes a backing plate which supports the seal. Three springs work in conjunction to apply the proper resultant force vector to urge the seal against the rollers. A compression spring is oriented normally to the backing plate and fits between the sideframe and backing plate. The compression spring biases the seal against the end face of the form roller. A torsion spring is attached to the backing plate just above the seal and urges the seal downward against a bend in the backing plate and the outside diameter of the metering roller. An extension spring is attached between a lower portion of the backing plate and a tab protruding from the side frame to under the metering roller, thereby urging the bottom portion of the seal toward the line of contact between the form roller and the metering roller. Because of the construction and spring arrangement of the prior art end-seal carrier described herein above, it is not readily removable from the sideframe of the dampener. In fact, the entire dampener must be disassembled from the printing press in order to remove the prior art end-seal carrier.
Although the above described end-seal carrier assembly has been found to function satisfactorily for the dampener disclosed in the '938 patent, there are a number of disadvantages associated with it that have, for example, limited further advancements in seal-type continuous dampeners. One such disadvantage is the necessity in the prior art configuration to include a lower extension spring to urge the lower portion of the backing plate, and consequently the lower portion of the seal, toward the line of contact between the form roller and the metering roller.
Further disadvantages include the need to continually clean the extension spring since its location assures that it is constantly subjected to becoming fouled by ink, paper dust, and offset powder. In addition, since the end-seal carrier cannot be readily removed from the dampener, it is particularly difficult to configure a dampener based on the '938 patent to fit a large printing press in that such a press requires removable rollers and the end-seal carriers obstruct such roller removal. Yet another disadvantage of the prior art end-seal carrier is the lack of flexibility in configuring the profile of the sideframes of the dampener since the spring tabs must be attached to the sideframes and located immediately beneath the metering roller.